1. Field of the Invention
The present invention relates to a pressure relief system for use in live well snubbing.
2. Description of the Related Art
For the insertion of piping and tools into live well bores, and the extraction of piping and tools from live well bores, known as "snubbing", it is conventional to employ a snubbing unit provided with one or more blow-out preventers (BOPs), which are closed into pressuretight engagement with the piping in order to prevent leakage of gas under pressure from the well bore.
During conventional snubbing operations, it is considered standard procedure to operate at the available surface pressure. For example, for a well having 4,500 psi surface pressure, then this pressure would typically be consistently maintained at the uppermost blow-out preventer while performing snubbing or stripping operations through annular BOPs.
The present invention is based on the concept that it would be desirable to reduce the pressure between the well bore and the apparatus employed for snubbing, thereby reducing unnecessary risks and improving the safety of what would otherwise normally be considered to be a very hazardous operation, i.e. moving pipe through blow-out preventers at a pressure differential of 4,500 psi